Tool location in automatically controlled machine tools



Feb. 22, 1966 WILLIAMSON Re. 25,956

TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS Original FiledJuly 22, 1963 3 Sheets-Sheet 1 Indian.

WW m x bur Feb. 22, 1966 w so Re. 25,956

TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS Original FiledJuly 22, 1963 3 Sheets-Sheet z INVEAJHL I 90m ism/244,, 9

5 Sheets-Sheet 3 D. T. N. WILLIAMSON Feb. 22, 1966 TOOL LOCATION INAUTOMATICALLY CONTROLLED MACHINE TOOLS Original Filed July 22,

United States Patent 25,956 TOOL LOCATION IN AUTOMATICALLY CONTROLLEDMACHINE TOOLS David Theodore Nelson Williamson, London, England,assignor to The Molins Organisation Limited, a British company OriginalNo. 3,171,327, dated Mar. 2, 1965, Ser. No.

296,763, July 22, 1963. Application for reissue July 22,

1965, Ser. No. 475,626 Claims priority, application Great Britain, July27, 1962,

28,962/62 6 Claims. (CI. 90-11) Matter enclosed in heavy bracketsappears in the original patent but forms no part of this reissuespecification; matter printed in italics indicates the additions made byreissue.

This invention concerns improvements in or relating to a method of andapparatus for selecting and locating a cutting tool in a cutter head ofa numerically controlled machine tool.

Present day practice in the engineering industry tends to lead to theproduction of components on a large scale. Where such components aremade from metal which is to be machined, cut or fashioned to therequired shape, it has become usual to perform successive operations ondifferent machines, each of which has been tooled and set up for thatone particular operation. The workpiece may be transferred from machineto machine after each operation, either manually or automatically, untilthe whole machining or fashioning process has been completed. Themachine tools may be numerically or programme controlled since this hasled to cost economies due to reduced machining time.

Whilst this practice is suitable for components to be produced in largebatches, it may prove uneconomic if the required quantity is small orrelatively small, since then the setting-up time becomes large inrelation to the total machining time. It might in some cases be possibleto revert to manually controlled multi-purpose machine tools for smallbatches but usually this increases costs due to increased machining timeand, possibly, to additional inspection requirements. It has, thereforebeen proposed to use a multi-purpose numerically controlled machine toolcapable of carrying out as many machining operations as possible and itis believed that this may help to reduce costs for batches of.components to be produced in small quantities or even singly.Accordingly, the setting-up time should be as short as possible. It,therefore, becomes desirable to have the machine tool designed to beable to change cutting or other types of tool as quickly as possiblewhen desired either during machining operation or on completion of onebatch and before starting another, and to be able to locate the selectedtool accurately within the machine tools cutter head.

The accurate location of the cutting tool within the cutter headpresents f-ew difficulties in two dimensions, i.e. those dimensions in aplane transverse to the axis of the cutting tool since it is grippedwithin a chuck or collet. The location in the third dimension i.e. alongits own axis, does cause difficulties since the length of the toolitself is only nominal whilst the act of being gripped may cause it tomove. Whilst small differences in the location of the tool end in thisdirection along its own axis may not be of any great importance forrough machining such as is involved in cleaning up the face of acasting, for contour milling such differences cannot be allowed exceptwith the design limits of the machine tool itself. Consequently it isdesirable to be able to locate the tool cutting end with a high degreeof accuracy in a direction along its axis, to say .0005 or better.

According to the present invention there is provided Reissued Feb. 22,1966 a method of gripping a selected tool from a plurality of tools andof locating it in a spindle of the cutter head of a numericallycontrolled machine tool, comprising the successive steps of: positioningthe cutter head and the plurality of tools so that the longitudinal axesof the spindle and the selected tool are aligned with the shank of theselected tool directed towards the cutter head; reducing the distancebetween the cutter head and the plurality of tools until the shank ofthe selected tool is inserted into the spindle; causing the shank to begripped in the spindle; withdrawing the selected tool by moving apartthe cutter head and the plurality of tools; repositioning the cutterhead opposite a surface of the machine tool; causing the shank to befree to move in the spindle; reducing the distance between the cutterhead and the surface to a desired value whereby the cutting end of thetool is abutting the surface; and causing the shank to be gripped in thespindle with its cutting end the same distance from the cutter head asthe said desired value.

The distance between the cutter head and the plurality of tools may bereduced to a figure whereby the distance of the cutting end of theselected tool from the cutter head exceeds the said desired value.

Further according to the invention there is provided a numericallycontrolled machine tool comprising a cutter head, a surface to which isfixed a workpiece, opposed to the cutter head, and a magazine adjacentthe surface containing a plurality of cutting tools having their shanksdirected towards the cutter head, the cutter head having a spindle inwhich is located a collet actuated to grip the shank of a selectedcutting tool and the surface having a datum pad against which thecutting end of the selected cutting tool is capable of being abutted.The collet may be actuated to close by the application of a force actingin the direction of the longitudinal axis of the selected cutting tool,the said force being transformed by the collet into a gripping forceacting normally to the shank of the selected cutting tool which isthereby maintained in a stationary position relative to the spindle.

Thus, it can be seen that the arrangement of the present invention issuch that the selected cutting tool and the workpiece are mounted inopposed relationship to each other such that relative rotation betweenthe same is provided to eficct the desired machining operation.

The magazine may comprise a series of openings, into each of which aholster fits, each holster being adapted to grip the cutting end of acutting tool, and may be fixed to the said surface and the holsters forman array in which shanks of the cutting tools housed therein projectparallel to each other.

The cutter head may be movable in a horizontal plane and the surface ismovable in a vertical plane.

Apparatus in accordance with the invention will now be described by wayof example with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of a numerically controlled machine tool,

FIGURE 2 is a section through the tool magazine shown in FIGURE 1,

FIGURE 3 is a section through a cutter head of the machine tool ofFIGURE 1, and

FIGURE 4 is a section on the line IVIV of FIG- URE 3.

The numerically controlled machine tool shown in FIGURE 1 consists of aslide table 101 carrying a cutter head 102 and of a vertical member 103to which is attached a work surface, in this case a pallet, 104. Thecutter head 102 possesses two degrees of freedom of movement, atraversing slide 105 for movement across the slide table 101 and a feedslide 106 which moves on and at right angles to the traversing slide105. The

cutter head 102 is integral with the feed slide 1.06 and is adapted tohold two cutting tools 107 and T which are inserted and gripped in amanner to be described hereinafter in quills 109 and 2. The pallet 104possesses one degree of freedom of movement, i.e. in a verticaldirection, and is attached to a vertical slide table 113 provided withten openings 114 facing towards the cutter head 102. Two workpieces 115and 116 are fixed to the work surface of the pallet 104 [and] so thatsaid tools 107, T and said workpieces 115, 116 are mounted in p- POA't'drcl't'ltionship to each other such that relative rotation between thesome is provided to effect the desired machining operation. Also mountedon the pallet 104 in a position lower down and to the right of theworkpieces there are two pads 117 and 118. The spacing between the twoworkpieces 115 and 116 and between the two pads 117 and 118 is the sameas that between the two quills 109 and 2. Thus the machine shown in FIG-URE l is suitable for machining two workpieces simultaneously. Thespacing of the openings 114 is similarly arranged. The space between thefirst opening and the sixth opening (numbering the openingsconsecutively from one side or the other) is the same as that betweenthe two quills 109 and 2 and is identical with that between the secondand seventh openings, the third and eighth, the fourth and ninth andbetween the fifth and tenth openings.

Automatic control mechanism is not shown in FIG- URE 1, although acontrol panel is indicated at 119. It is, however, of known designoperating on known principles embodying, for example, a punched ormagnetic tape containing operating instructions. In FIGURE 3 the quill 2is fixed to the casting l. A rotating spindle 3 is positioned within thequill 2, from which it is separated by two angular contact bearings 4and 5 and a plain ball bearing 6. A locating ring 7 is fixed to the boreof the quill 2 by means of dowels 8. Concave-convex washers 9, known asBelleville washers, separate an outer race 10 of the angular contactbearing 5 and the locating ring '7, and being compressed supply theforce necessary to preload the balls of the bearing 5 between the outerrace 10 and an inner race 11 machined around the spindle 3 and thus toprevent axial play. Tile bearing 4 has an outer race 12 which fits intothe bore of the quill 2. An inner race 13 is machined around the spindle3. A lock nut 14 is threaded over the quill 2 and bears against theouter race 12, thus supplying the force necessary to pro-load the ballsof the bearing 4. The bearing 4 is fitted to take away any forward axialthrust and the bearing 5 to take backward axial thrust. Oil mistlubrication is supplied to both bearings 4 and 5 through a hole 15 and acircumferential channel 16 in the quill 2. A guard ring 17 is threadedon the spindle 3 and provides a labyrinthine passage 18 between it andthe lock nut 14, thus preventing the entry of foreign matter withoutallowing excessive escape of oil.

The back end of the spindle 3 has a reduced diameter 19 and a shoulder20. A spacer 21 nips the inner race 22 of the ball bearing 6 against theshoulder and is held in position by a hub 23 of a pelton wheel 24. Theindividual buckets of the pelton wheel 24, which is a high speed wheeloperated by an oil jet, are secured to the hub 23 by a lock washer 25,which in its turn is locked into position by a nut 26 threaded over afurther reduced diameter 27 of the spindle 3. The outer race 28 of theball bearing 6 is held in position by a locking ring 29 secured to thequill. Lubrication for the bearing 6 is supplied by the oil mistpressure being transmitted through a clearance 30 between the spindle 3and the bore of the Belleville washers 9.

The front end of the spindle 3 is bored to mate with the front end of anose tub-e 34. The front peripheral end of the nose tube 34 forms atruncated cone, whilst internally it is provided with a shoulder 32 anda taper 33. Restraining means, a retaining ring 31 which for the sake ofassembly is split into four quadrants, is interposed between the bore ofthe spindle 3 and the truncated cone of the nose tube 34. The functionof the ring 31 is to cause the nose tube 34 to lock against the internaltaper of the spindle 3. Thus the nose tube 34 cannot move forwards whena forward axial force is applied to it. The back periphery of the nosetube 34 is a sliding fit within the bore of the spindle 3. A compressiontube 35 also forms a sliding fit within the bore of the spindle 3 and isprovided with an internal taper, the slope of which opposes that of thetaper of the nose tube 34. A collet 36 fits within the nose tube 34 andthe compression 35. The collet 36 has a front frustroconical end 37which mates with the internal tapers of the nose tube 34, and has a backfrustro-conical end 38, which mates with the internal taper of thecompression tube 35. A sleeve 39, provided with slits 40, fits insidethe collet 36. The front end of the sleeve 39 is held against theshoulder 32 of the nose tube 34 by the action of a spring 41 bearingagainst a shoulder 42 of the compression tube 35.

A cutting tool T fits within the sleeve 39', its back end having a dog43 which fits in a recess of a plunger 44. A push rod 45 is attached tothe plunger 44 by means of a pin 46. An enlarged portion of the plunger44 is fixed against relative rotary movement to the compression tube 35by a key 47. The plunger 44 is however, movable axially relative to thecompression tube 35, since the key 47 is slidable within elongatedkeyways. The plunger 44 is held in its front position by a spring 48bearing against a piston 49 which is slidable within the bore of thespindle 3. The space between the back of the piston 49 and a shoulder 50of the spindle 3 is occupied by Belleville washers 51. The assembly ofthe retaining ring 31, the nose tube 34, the collet 36, the compressiontube 35 and the piston 49 is such that the Belleville washers 51 are ina state of compression and thus act to force the compression tube 35forwards. The push rod 45 is slidable within a draw bar 52 which isintegral with the piston rod 49.

Both the push rod 45 and the draw bar 52 extend beyond the back end ofthe spindle 3 into a recess 53 within a hydraulic piston 54 which isslidable within a composite cylinder 55. A through piston rod 56 isintegral with the piston 54, with its front end drilled totake two pins57 and 58 (see FIGURE 2). The heads of the pins 57 and 58 are slidablein grooves 59 in a front cylinder head 60 of the cylinder 55. A bearingring 61 is threaded onto the back end of the draw bar 52, along whichits position is adjustable.

The cylinder comprises a barrel 62 to which is fixed the front cylinderhead and a back cylinder head 63. End plates 64 and 65 are fixedrespectively between the back cylinder head 63 and the barrel 62 andbetween the front cylinder head 60 and the barrel 62. 0 rings 66 sealthe cylinder area so that the hydraulic fluid is prevented from leakingto atmosphere. The front cylinder area is connected via a passage 67 inthe barrel 62 to a flexible hose 68 which communicates directly to a1,500 psi. hydraulic main. The back cylinder area com municates via apassage 69 to a flexible hose 70 which can be connected through athree-way selector (not shown) to the 1,500 psi hydraulic main or to atank.

The back end of the piston rod 56 is provided with an extension 71 whichprojects through a bracket 72 attached to the casting 1. A spring 73urges the piston rod 56 forwards and bears between the bracket 72 and ashoulder 74. Forward movement of the piston rod 54 is restricted by acirclip 75 in the extension 71 coming into contact with the bracket 72.

A second push rod 76 extends through the piston rod 56 and is providedwith a pusher face 77 at its back end. The pusher face is operable tomove two arms, only one of which, 78, can be seen in FIGURE 1. The twoarms 78 swing about pivots 79 fixed to the casting 1 and in movinganti-clockwise about their pivots 79 trip microswitches 80, of whichonly one again can be seen in FIGURE 1. A stop 81 attached to the backcylinder head 63 prevents the second push rod 76 being moved forwardbeyond a preset position by a spring 82 held in tension between thebracket 72 and the arms 78, the object of the spring 82 being to keepthe arms 78 and the pusher face 77 in contact.

FIGURE 2 shows a section through the vertical slide 113 which isprovided with rails 146 to take a magazine 147. The back of the magazine147 slides on the rails 146 and its far end locks against an end stopfor positive location on the vertical slide 113, the end stop andlocking mechanism not being shown. Opposite each of the ten openings 114an aligned hole 148 in the magazine 147 is adapted to hold a holster149. The holster 149 is flanged at 150 to locate it against the back ofthe magazine 147 and is pinned (not shown in FIGURE 4) to prevent itmoving against the vertical slide 113.

A tool-holder 151 has a shoulder 152 which is a snug fit in the holster149. Between the shoulder 152 and a lip 153 of the holster 149 is aspring 154 which holds the tool-holder 151 firmly against a pin 155. Thetool-holder 151 is provided with a thin-walled projection 156 into whichthe cutting end of the tool T is pushed. The bore of the thin-walledprojection 156 is made to be an interference fit with the diameter ofthe tool T, say 0.004 smaller. Since the tool 108 has two cutting flutes157 only there will be two point contact in any plane at right angles tothe tools longitudinal axis between the tool T and the projection 156.The thin wall enables the projection to take up an appropriate set andthus to grip the tool T firmly. The tool holder 151 is made from asuitable plastic.

A guard 158 carried in a frame 159 is hinged to the top of the verticalslide 113 at 160. The guard 158 has to be opened for changing orselecting a cutting tool, this opening being carried out automaticallyby a stationary ramp which lifts it when the vertical slide 113 islowered to a position where the longitudinal axes of the cutting toolsand the quills 109 and 2 are aligned. The ramp is not shown in FIGURE 2.

In operation, the pallet 104 containing two workpieces 115 and 116 andthe magazine 147 containing a suitable quantity of cutting tools tocarry out the requisite machining operations on the workpieces, are fedby hand to the machine and are located on the vertical slide table 113.Since the machine is provided with twin quills 109 and 2 for operatingsimultaneously on the two workpieces 115 and 116 it will be seen thateach operation must be duplicated. In the description following only onequill 2 and one workpiece 116 will be dealt with, it being understoodthat the other quill 109 duplicates all movements and operations. Whenthe pallet 104 and the magazine 147 are in position the machine is readyto start its automatic operation.

Programmed instructions in the form of a tape are fed to the controlconsole, which is not shown, detailing the first cutting tool T to beused on the workpiece 116, its position in the magazine 147 and thenominal length of its cutting end. The actual length differs from thenominal length by the amount the cutting tool has been previously groundor by an amount representing normal manufacturers tolerances. Servomechanisms which are not shown in the drawings, being of known designand application, operate to lower the vertical slide table 113 until theaxes of the cutting tool T and of. the quill 2 are in the samehorizontal plane, and to traverse the feed slide 106 until the two axesare in the same vertical plane. By the time the cutter head and themagazine are in this position it is essential that the spindle 3 shouldhave ceased to rotate. A brake of known design and not shown in any ofthe figures is incorporated to stop the spindle 3 and is actuated by apositional microswitch when the vertical slide table 113 has beenlowered so that the axes of the cutting tool T and of the quill 2 are inthe same horizontal plane. As the vertical slide table 113 is loweredthe guard 158 (FIGURE 2) is raised by means of the ramp which is notshown.

While the cutter head is moving, instructions carried on a tape activatethe chuck to open. The three-way selector (which is not shown) connectsthe flexible hose 70 to tank. The pressure difference between the frontand back sides of the cylinder causes it to move forward until the frontend of the front cylinder head comes to rest against the back end of thenut 26. During this last movement the force exerted by the spring 73 onthe piston rod 56 is sufficient to hold the piston 54 at rest andtherefore to cause the cylinder 55 to move. As soon as the cylinder 55comes to rest, the piston 54 starts to move backwards. As the piston 54moves, the pins 57 and 58 move with it, until they come to bear againstbearing ring 61 which then moves backwards. The total backward movementof the bearing ring 61, of the draw bar 52 and the piston 49, whichmoves with it, is of the order of .020". This movement is sufficient tocompress the Belleville washers 51 further and thus to remove theforward acting force exerted by the piston 49 on the compression tube35. As soon as this forward acting force is removed, its radialcomponent acting through the frustro-conical ends 37 and 38 of thecollet 36 on the slit sleeve 39 is also removed. The sleeve 39 is thusallowed to expand to its uncompressed diameter and the chuck is open.

When the chuck is open and the spindle 3 and the tool shank are alignedto within .003", the cutting head moves forward i.e. towards themagazine 147 to a predetermined position. The predetermined positionvaries with the effective length of the cutting tool selected and isregulated by the taped instructions. As the cutting head moves forwardthe shank of the tool is inserted into the sleeve 39. The spindle 3 isrotated slowly by cracking the com trol value to the hydraulic fluid jet(neither of which are shown) operating the pelton wheel 24. As soon asthe dog 43 engages in the corresponding recess in the plunger 44, thespindle 3 is brought to rest. The three-way selector then admitspressure to the flexible hose and thus to the position of the cylinder55 behind the piston 54. Due to the greater cross-sectional area of theback portion of the piston 54, it moves forward until its front endcomes to rest against the front end plate 65. Forward movement of thepiston 54 and the piston rod 56 allows the draw bar 52 and the piston 49to move forward. By the time the piston 54 and the cylinder 55 come torest due to the circlip coming into contact with the bracket 72, theBelleville washers 51 are again exerting the designed forward thrust onthe piston 49. This thrust is transmitted directly to the compressiontube 35. Due to the back frusto-conical end 38 of the collet 36 and themating portion of the bore of the compression tube 35 this thrust istransferred into a skin force normal to the two surfaces. The normalforce then has two components, a force directed radially inwards overthe circumference of the back frustro-conical end 38 of the collet 36and a forward force directed over the cylindrical portion of the collet36. The forward force is similarly divided into two components due tothe front frusto-conical end 37 and the mating portion of the bore ofthe nose tube 34, a radially inward force acting around thecircumference of the front frusto-conical end 37 and a forward axialforce. This latter forward axial force acts to wedge the frontfrusto-conical end 37 into the taper 33 of the nose tube 34 and to wedgethe retaining ring 31 between the nose tube 34 and the mating portion ofthe spindle 3. Thus there are two radially inward directed forces actingon the slit sleeve 39. These forces partially close up the slits 40 andreduce the diameter of the sleeve 39 so that the tool T is grippedsufficiently tightly to resist the torque necessary for cutting. Theradial forces cannot move the sleeve 39 axially, whilst any axialmovement due to frictional force between the collet 36 and the sleeve 739 is resisted by the sleeve 39 being in contact with the shoulder 32 ofthe nose tube 34. The sleeve 39 thus remains stationary relative to thespindle 3 whilst gripping the tool T.

After the tool T is gripped the cutter head 102 moves away from themagazine withdrawing the tool T from the tool holder 151. The verticalslide table 113 rises and the slide 105 traverses until the centre ofthe surface 118 is approximately aligned with the longitudinal axis ofthe cutting tool T when both movements stop. The cutter head 102 thenfeeds forward on the slide 105 until it is a predetermined distancewhich is dependent on the nominal length of the cutting portion of thecutting tool T, from the surface 118 when it stops. Whilst it is movingtowards the surface 118 the chuck opens as described hereinafter so thatthe tool T is movable along its axis relative to the spindle 3. Thepredetermined distance is dependent on taped instructions and differsfor each nominal length of cutting tool. It is, however, always lessthan the nominal length so that as the cutting head approaches thepredetermined position the front end of the tool comes to rest againstthe datum surface. Further forward movement of the cutting head leads tothe tool moving backwards relative to the spindle 3 and to backwardmovement of the plunger 44 against the action of the spring 48 and ofthe push rod 45. Since the chuck is open, the cylinder 55 is in itsforward position thus reducing the gap between the push rod 45 and thesecond push rod 76. Backward movement of the push rod 45 is thereforetransmitted to the second push rod 76 which in its turn moves the arms78 in an anti-clockwise direction about their pivots 79. Thepredetermined distance and the nominal length of the tool are chosen andcalculated so that anti-clockwise movement of the arms 78 makes contactin one only of the microswitches 80. the wrong tool is selected eitherboth microswitches make contact or neither do, the former in the case ofa tool having too great a nominal length and the latter when the nominallength is too small. Only when the correct microswitch has made contactwill the machine tool continue to accept and carry out subsequent tapedinstructions. Thus the possibility of damage is safeguarded should atool of incorrect length be gripped.

After the completion of the machining operation the cutting head and theempty tool storage position on the pallet are again aligned. The cuttinghead moves forward in the Z plane, the chuck opens and the tool isinserted into the tool storage where it is gripped. The cutting headmoves backwards, the tool is left behind, and plunger 44 moves forwardunder the action of the spring 48. The cutting head is now in readinessto pick up the next tool for the following machining operation.

Although a machine tool has been described as shown in FIGURE 1, theinvention is equally applicable to other forms. For instance thevertical worktable might be rotatable while the cutter head might alsobe capable of being swivelled through 90. In this instance there wouldbe, of course, only one quill and one workpiece.

What I claim as my invention and desire to secure by Letters Patent is:

l. A numerically controlled machine tool comprising a cutter head, asurface to which is fixed a workpiece ill opposed to the cutter head.and a magazine adjacent the surface containing a plurality of cuttingtools having their shanks directed towards the cutter head, the cutterhead having a spindle in which is located a collet actuated to close andto grip thereby the shank of a selected cutting tool and the surfacehaving a datum pad against which the cutting end of the selected cuttingtool is capable of being abutted so that the distance of the cutting endof the selected cutting tool is a predetermined distance from the cutterhead.

2. A numerically controlled machine tool as claimed in claim 1, in whichthe collet is actuated to close by the application of a force acting inthe direction of the longitudinal axis of. the selected cutting tool,the said force being transformed by the collet into a gripping forceacting normally to the shank of the selected cutting tool which isthereby maintained in a stationary position relative to the spindle.

3. A numerically controlled machine tool as claimed in claim 1, in whichthe magazine comprises a series of openings, into each of which aholster fits, each holster being adapted to grip the cutting end of acutting tool.

4. A numerically controlled machine tool as claimed in claim 3, in whichthe magazine is fixed to the said surface and the holsters form an arrayin which the shanks of the cutting tools housed therein project parallelto each other.

5. A numerically controlled machine tool as claimed in claim 1, in whichthe cutter head is movable in a horizontal plane and the surface ismovable in a vertical plane.

6. A numerically controlled machine tool comprising a tool-holdingmember, a workpiece opposed to raid toolholding member, a magazinecontaining a plurality of cutting tools having their shanks directedtowards the too-I- hOlding mcmbcr the tool-holding member havingtoolgripping means adapted to be actuated to close and to grip therebythe shank of the selected cutting tool from among said plurulit ,v,means to provide relative rotation between said workpiece and saidselected cutting tool to eflect the machining operation, and a datumsurfacc against which the cutting curl of said selected cutting tool iscapable of being abuttcd so that the distance of said cutting and ofsaid selected cutting tool is a predetermined distance from thel0ol-holding member.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS 1,208,852 l2/19l6 Sproul.

2,326,848 8/1943 Fanning.

2,901,927 9/1959 Morgan 774 2,927,703 3/1960 Raincy et al. 295683,064,502 l1/l962 Pittwood 29568 3,124,976 3/1964 Pittwood 77-4 \VILLIAMW. DYER, JR., Primary Examiner.

L. VLACl-IOS, Assistant Examiner.

